Recently, a high luminance and high power light emitting semiconductor device, and a small sized and high sensitivity light emitting device are developed and are utilized in various fields. Such light emitting devices are utilized, for example, to make light sources of heads for the light printer, light sources for backlights of the liquid crystal displays, light sources for kinds of meters, sensors for kinds of reading, etc.
Such a light emitting device is shown in FIG. 13 as an example. The plastic package 35 which has a recess and lead electrodes 32 is used and an LED chip 31 is mounted (die bonding) on the exposed surface of one lead electrode 32. The electrodes of the LED chip 31 are bonded to the lead electrode 32 by gold wires 34, respectively. The LED chip mounted in the recess is sealed with a transparent molding resin 39. With this configuration, the light emitting devices having very high reliability can be obtained.
However, such light emitting devices will be required to withstand more severe environment as their applications expand. The light emitting devices in air planes and automobiles are subjected to low-temperature conditions lower than −20° C. or high temperature conditions higher than +80° C. and are subjected to thermal shock or changed pressures. In such cases, the intensity or the directivity of the light outputted from the device is changed by exfoliation of the LED chip from the die-bonding resin generated by expanding and contraction of the mold resin. The light then disappears completely by the breaking of the wire at worst.
In the light emitting element, the heat is generated by the consumption of electricity. The heat generated by the light emitting element may be transmitted through the lead electrodes to the substrate in the light emitting devices.
However, that heat radiation is not enough. Therefore, the speed of response (operation) of the element and the resin covering the element deteriorate by raising the temperature of the light emitting element arose from insufficiently heat radiation.
To avoid such problems, the can-type packages are used conventionally.
For example, a stem shown in FIG. 12 is used in a conventional light emitting device. The stem has a convex metal base 40 and lead electrode pins 32 penetrating the through halls of the metal base 40 so as to seal by an insulating material 33(for example glass). The light emitting element 31 is connected on the stem electrically and hermetically sealed with can 41 having a flange 36 in bottom side and a window 37.
Such light emitting devices can prevent the wires from disconnecting and have high reliability, good moisture resistance, good heat radiation characteristic and good thermal stability, since the packages are made of metal and have hollow structure.
However, surface mounting type light emitting devices are required instead of the lead type light emitting devices recently, as thin-sizing and small-sizing advance to respond to the requirements of high density assembly.